This invention relates to the degradation of organic pesticides, notably aromatic compounds such as chlorinated aromatics, by ferric reagents to form inorganic wastes.
Chlorinated hydrocarbon, organophosphorus, organonitrogen, organometallic, and the like pesticide compounds number among the hazardous wastes that require special methods for disposal because of their toxic, refractory, or persistent properties. Many of these compounds that do not degrade pose a threat to biota and/or human populations. Concern about the potential hazards associated with the compounds has resulted in numerous recent laws and policies that require the cleanup of contaminated soil, sediments, surface water, and wastewater.
A number of disposal techniques have been suggested for various types of these toxic chemicals (see reviews by Munnecke, D. M., 70 Residue Rev. 1-26 (1979) and Ehart, O. R., 1985 National Workshop on Pesticide Waste Disposal Proceedings EPA/600/9-85/030, pages 2 to 11 . Physical methods include entrapment, burial, adsorption, flocculation, and the like (reviewed by Nye, J. C., 1985 National Workshop on Pesticide Waste Disposal Proceedings, cited above, pages 43 to 480); an example is the activated charcoal detoxification of pesticides disclosed by Scott in U.S. Pat. No. 4,585,753. Chemical methods include oxidation, reduction, hydrolysis, conjugation, irradiation, and the like (reviewed by Honeycutt, R. C., 1985 National Workshop on Pesticide Waste Disposal Proceedings, cited above, pages 72 to 85); examples include incineration (discussed by Ferguson, T. L., and Wilkinson, R. R., in Krueger, R. F., and Seiber, J. N., eds., Treatment and Disposal of Pesticide Wastes, ACS, 1984, chapter 11, pages 181 to 191), thiosulfate oxidation using hydrogen peroxide and copper disclosed by Walton and Rutz in U.S. Pat. No. 4,569,769, and the microwave plasma detoxification process described in Bailin, L. J., et al., 12 Environ. Sci. Techn ol. 673-679 (1978). Biological methods include degradation by enzymes and microorganisms (Schmidt, C., 1986 National Workshop on Pesticide Waste Disposal Proceedings, EPA/600/9-87/001, pages 45 to 52, and Johnson, L. M., and Talbot, H. W., 39 Experientia 1236-1246 (1983)).
Waste treatment systems employing Fenton's reagent, i.e., hydrogen peroxide containing ferrous ions, have been suggested for the degradation of chlorobenzene, phenols, formaldehyde, s-triazine herbicides and octachloro-p-dibenzo-dioxin (Plimmer, J. R., et al., 19 J. Agr. Food Chem. 572-573 (1971), Watts, R. J., et al., Extended Abstracts #198th ACS Meeting, Env. Chem. Div., 1989, pages 346-349, and Sedlak, D. L., and Andren, A. W., 25 Environ. Sci. Technol. 777-782 (1991)). Treatment of hazardous wastes with Fenton's reagent "has its limitations. Non-polar organic molecules like polycyclic aromatics, benzene, mesitylene or hydrocarbons with long carbon chains are especially difficult to destroy" (Eul, W., et al., "Hydrogen Peroxide-Based Treatment Technology for Hazardous Waste," Emerging Technologies in Hazardous Waste Management, ACS Symposium No. 422, 1990, 1-35 at 29).
Iron hydroxide finely dispersed on inorganic supports that are unreactive to HO.degree., including silica and montmorillonite clay, have been disclosed to improve the efficiency of waste water treatments using H.sub.2 O.sub.2 (Mill, T., and Haag, W. R., Preprints of Extended Abstracts, 198th Nat. Meeting Amer. Chem. Soc., Div. Env. Chem., A.C.S., Washington, 1969, paper 155, pp. 342-345). Phenol has been photocatalytically oxidized in the presence of hydrogen peroxide and titanium dioxide powders in the presence and absence of ferric ions (Wei, T. Y., et al., J. Photochem. Photobiol. A: Chem., 55: 115-126 (1990). Dilute aqueous formaldehyde waste solutions have been neutralized by ferric chloride and hydrogen peroxide in a process developed for treating Bureau of Reclamation reverse osmosis desalting membrane storage solutions (Murphy, A. P., et al., 23 Environ. Sci. Technol. 166-169 (1989)). However, Barbeni, M., et al., found the addition of ferric ions instead of ferrous inconsequential in the chemical degradation of chlorophenols by Fenton's reagent (16 Chemosphere 2225-2237 (1987) at 2229 and FIG. 4 on 2232).